how to define fcc for bulk molecule system

Dear all,

I intend to calculate the shear viscosity of a box of liquid molecules. When setting up the fix/deform, fix/ave spatial commands, I was asked to set up a lattice. Since my system is a cubic box filled with a liquid mixture, which kind of lattice should I set up so that I can calculate the shear viscosity? Is lattice fcc 0.5 OK for that? Thanks a lot.

Laura

2011/8/30 zhangliqun <[email protected]>:

Dear all,

I intend to calculate the shear viscosity of a box of liquid molecules. When
setting up the fix/deform, fix/ave spatial commands, I was asked to set up a
lattice. Since my system is a cubic box filled with a liquid mixture, which
kind of lattice should I set up so that I can calculate the shear viscosity?
Is lattice fcc 0.5 OK for that? Thanks a lot.

no, you _don't_ need to set up a lattice.
please re-read the documentation carefully.
most likely you want to use the "units box"
option instead of the default of "units lattice".

RTFM rulez!

cheers,
    axel.

Thanks a lot for reminding. But without defining the lattice, I got such kind of error:

ERROR: Use of fix ave/spatial with undefined lattice

since I need to use fix ave/spatial to record veloctiy profile. How to do with that? Thanks again.

2011/8/30 zhangliqun <[email protected]>:

Thanks a lot for reminding. But without defining the lattice, I got such
kind of error:

NO! i repeat, you _DON'T_ need to define a lattice.
all you need to do is to tell all those fixed to NOT
use lattice units, which is _VERY_ likely what you
want (and expect) in any case.

ERROR: Use of fix ave/spatial with undefined lattice

since I need to use fix ave/spatial to record veloctiy profile. How to do
with that? Thanks again.

please RTFM again!!
if you do it properly, you will see.

if you refuse to properly read the documentation,
nobody will want to help you in the future.

axel.

Thank you for insisting. I found out what to do with fix ave/spatial. In fact, I did reply to you and the lammps-users as you can see…

All the lattice command does for many other commands is
define another (sometimes more convenient) length scale,
in terms of the lattice rather than the box. All commands
that need that length scale allow you to add "units box"
as an option, in which case you don't need to define a lattice.
Fix ave/spatial is one of those.

Steve